Concerns with Sampling and Observational Studies

Question 1

Selection Bias
* Even when a random sampling design is used, there are other
potential sources of bias in the sampling method.
* Consider that there are three steps in a sampling process

Answer 1

. Constructing the sampling frame
2. Selecting individuals from the frame for the sample (sampling design)
3. Contacting the individuals in the sample to collect responses

Question 2

Selection bias

Answer 2

Selection bias occurs when individuals in the target population are
not sampled at an equal rate.

Question 3

Undercoverage

Answer 3

occurs when a certain group of individuals in the
target population is not included in the sampling frame and therefore
given no chance of selection in the sample

Question 4

Overcoverage

Answer 4

occurs when a certain group of individuals not in the
target population is included in the sampling frame

Question 5

Nonresponse

Answer 5

occurs when individuals selected for the sample cannot
be contacted or refuse to participate in the study.

Question 6

Missing completely at random (MCAR):

Answer 6

When the probability of
nonresponse is the same for all individuals in the sample, we say that
the nonrespondents are missing completely at random

Question 7

Missing at random (MAR):

Answer 7

When the probability of nonresponse is
associated with known and measured factors, we say that the
nonrespondents are missing at random.

Question 8

MAR assumes that certain groups in the population

Answer 8

more likely to
produce nonresponse than others

Question 9

MAR assumes that certain groups in the population are more likely to
produce nonresponse than others.
* If these groups are known prior to sampling, then we can

Answer 9

oversample them,
or sample at a higher-than-representative rate, to guarantee proper
representation in the sample.
* After sampling, we can also adjust the weights assigned to individuals in the
sample to guarantee proper representation.

Question 10

Missing not at random (MNAR):

Answer 10

when the probability of
nonresponse varies for reasons that are unknown to us, particularly
the level of the variable of interest, we say that the nonrespondents
are missing not at random

Question 11

Weighting

Answer 11

is a procedure that allows us
to place a higher or lower emphasis on
certain individuals in the sample.

Question 12

An observational study

Answer 12

An observational study observes individuals and measures variables of
interest, without controlling any factors that might influence the responses

Question 13

An experimental study

Answer 13

An experimental study deliberately imposes some treatment on individuals in
order to observe their responses.

Question 14

Response bias

Answer 14

occurs when people answer falsely or inaccurately, sometimes
due to unintentional behavior by the interviewer.

Question 15

There are certain types of bias innate to an observational study:
* Response bias can also occur due to the wording of questions.

Answer 15

Questions may be:
* Leading (causing the respondent to favor one answer)
* Confusing
* Poorly defined